Uses of combinations (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine in methods of treating movement disorder

ABSTRACT

The invention relates to pharmaceutical compositions containing both (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine and their therapeutic uses, for example in the treatment of movement disorders, such as Tourette&#39;s syndrome.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/515,930, filed on Jun. 6, 2017, and to Great Britain Application No.1705304.2, filed on Apr. 1, 2017. The entire contents of each of theprior applications are hereby incorporated herein by reference.

This invention relates to pharmaceutical compositions containing both(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine and theirtherapeutic uses, for example in the treatment of movement disorders,such as Tourette's syndrome.

BACKGROUND OF THE INVENTION

Movement disorders can generally be classified into two categories:hyperkinetic movement disorders and hypokinetic movement disorders.Hyperkinetic movement disorders are caused by an increase in muscularactivity and can cause abnormal and/or excessive movements, includingtremors, dystonia, chorea, tics, myoclonus and stereotypies.

Hyperkinetic movement disorders often are often psychological in natureand arise through improper regulation of amine neurotransmitters in thebasal ganglia.

A particular hyperkinetic movement disorder is Tourette's syndrome,which is an inherited neurological condition characterised by multiplephysical and vocal tics. The tics are usually repetitive, but random,physical movements or vocal noises.

The vocal tics can be of various forms and include repeating one's ownwords, the words of others or other sounds. Onset usually occurs inchildren and continues through to adolescence and adulthood.

While the tics associated with Tourette's syndrome are temporarilysuppressible, those affected can usually only suppress their tics forlimited time periods. There is yet to be an effective treatment to coverall types of tics in all patients, but certain medicaments for ticsuppression have been developed.

It is known that dopamine receptor antagonists display an ability tosupress tics in Tourette's syndrome patients and a number dopaminereceptor antagonists are currently used in the suppression of Tourette'stics, such as fluphenazine, haloperidol and pimozide.

Type 2 vesicular monoamine transporter (VMAT2) is a membrane proteinresponsible for the transportation of monoamine neurotransmitters, suchas dopamine, serotonin and histamine, from cellular cytosol intosynaptic vesicles. Inhibition of this protein hinders presynapticneurons from releasing dopamine, resulting in a depletion of dopaminelevels in the brain.

VMAT2 inhibitors can be used to treat the symptoms of Tourette'ssyndrome.

Tetrabenazine (Chemical name:1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-3-(2-methylpropyl)-2H-benzo(a)quinolizin-2-one)has been in use as a pharmaceutical drug since the late 1950s. Initiallyused as an anti-psychotic, tetrabenazine is currently used for treatinghyperkinetic movement disorders such as Huntington's disease,hemiballismus, senile chorea, tic, tardive dyskinesia and Tourette'ssyndrome, see for example Jankovic et al., Am. J. Psychiatry. (1999)August; 156(8):1279-81 and Jankovic et al., Neurology (1997) February;48(2):358-62.

The primary pharmacological action of tetrabenazine is to reduce thesupply of monoamines (e.g. dopamine, serotonin, and norepinephrine) inthe central nervous system by inhibiting the human vesicular monoaminetransporter isoform 2 (hVMAT2). The drug also blocks post-synapticdopamine receptors.

The central effects of tetrabenazine closely resemble those ofreserpine, but it differs from reserpine in that it lacks activity atthe VMAT1 transporter. The lack of activity at the VMAT1 transportermeans that tetrabenazine has less peripheral activity than reserpine andconsequently does not produce VMAT1-related side effects such ashypotension.

Tetrabenazine is an effective and safe drug for the treatment of avariety of hyperkinetic movement disorders and, in contrast to typicalneuroleptics, has not been demonstrated to cause tardive dyskinesia.Nevertheless, tetrabenazine does exhibit a number of dose-related sideeffects including causing depression, parkinsonism, drowsiness,nervousness or anxiety, insomnia and, in rare cases, neurolepticmalignant syndrome, see for example the introductory section ofWO2016/127133 (Neurocrine Biosciences).

The chemical structure of tetrabenazine is as shown below.

The compound has chiral centres at the 3 and 11 b carbon atoms and hencecan, theoretically, exist in a total of four isomeric forms, as shownbelow.

The stereochemistry of each isomer is defined using the “R and S”nomenclature developed by Cahn, Ingold and Prelog, see Advanced OrganicChemistry by Jerry March, 4th Edition, John Wiley & Sons, New York,1992, pages 109-114. In this patent application, the designations “R” or“S” are given in the order of the position numbers of the carbon atoms.Thus, for example, RS is a shorthand notation for 3R,11bS. Similarly,when three chiral centres are present, as in the dihydrotetrabenazinesdescribed below, the designations “R” or “S” are listed in the order ofthe carbon atoms 2, 3 and 11b. Thus, the 2R,3S,11bS isomer is referredto in short hand form as RSS and so on.

Commercially available tetrabenazine is a racemic mixture of the RR andSS isomers and it would appear that the RR and SS isomers are the mostthermodynamically stable isomers.

Tetrabenazine has somewhat poor and variable bioavailability. It isextensively metabolised by first-pass metabolism, and little or nounchanged tetrabenazine is typically detected in the urine. It is knownthat at least some of the metabolites of tetrabenazine aredihydrotetrabenazines formed by reduction of the 2-keto group intetrabenazine.

Dihydrotetrabenazine (Chemical name:2-hydroxy-3-(2-methylpropyl)-1,3,4,6,7,11b-hexahydro-9,10-dimethoxy-benzo(a)quinolizine)has three chiral centres and can therefore exist in any of the followingeight optical isomeric forms:

The synthesis and characterisation of all eight dihydrotetrabenazineisomers is described by Sun et al. (Eur. J. Med. Chem. (2011),1841-1848).

Of the eight dihydrotetrabenazine isomers, four isomers are derived fromthe RR and SS isomers of the parent tetrabenazine, namely the RRR, SSS,SRR and RSS isomers.

The RRR and SSS isomers are commonly referred to as “alpha (a)”dihydrotetrabenazines and can be referred to individually as(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine respectively.The alpha isomers are characterised by a trans relative orientation ofthe hydroxyl and 2-methylpropyl substituents at the 2- and 3-positions —see for example, Kilbourn et al., Chirality, 9:59-62 (1997) and Brossiet al., Helv. Chim. Acta., vol. XLI, No. 193, pp1793-1806 (1958.

The SRR and RSS isomers are commonly referred to as “beta (β)” isomersand can be referred to individually as (+)-β-dihydrotetrabenazine and(−)-β-dihydrotetrabenazine respectively. The beta isomers arecharacterised by a cis relative orientation of the hydroxyl and2-methylpropyl substituents at the 2- and 3-positions.

Although dihydrotetrabenazine is believed to be primarily responsiblefor the activity of the drug, there have been no studies published todate that contain evidence demonstrating which of the variousstereoisomers of dihydrotetrabenazine is responsible for its biologicalactivity. More specifically, there have been no published studiesdemonstrating which of the stereoisomers is responsible for the abilityof tetrabenazine to treat movement disorders such as Tourette'ssyndrome.

Schwartz et al. (Biochem. Pharmacol. (1966), 15: 645-655) describesmetabolic studies of tetrabenazine carried out in rabbits, dogs andhumans. Schwartz et al. identified nine metabolites, five of which wereunconjugated and the other four of which were conjugated with glucuronicacid. The five unconjugated metabolites were the alpha- andbetα-dihydrotetrabenazines, their two oxidised analogues in which ahydroxyl group has been introduced into the 2-methylpropyl side chain,and oxidised tetrabenazine in which a hydroxyl group has been introducedinto the 2-methylpropyl side chain. The four conjugated metabolites wereall compounds in which the 9-methoxy group had been demethylated to givea 9-hydroxy compound. The chirality of the various metabolites was notstudied and, in particular, there was no disclosure of the chirality ofthe individual α- and β-isomers. Scherman et al., (Mol. Pharmacol.(1987), 33, 72-77 describes the stereospecificity of VMAT2 bindingbetween racemic α- and β-dihydrotetrabenazine. They reported thatα-dihydrotetrabenazine had a 3- to 4-fold higher affinity for theChromaffin Granule Monoamine Transporter than the β-isomer, when studiedin vitro. However, Scherman et al. does not disclose the resolution ortesting of the individual enantiomers of the α- andβ-dihydrotetrabenazines.

Mehvar et al. (J. Pharm. Sci. (1987), 76(6), 461-465) reported a studyof the concentrations of tetrabenazine and dihydrotetrabenazine in thebrains of rats following administration of either tetrabenazine ordihydrotetrabenazine. The study showed that despite its greaterpolarity, dihydrotetrabenazine was able to cross the blood-brainbarrier. However, the stereochemistry of the dihydrotetrabenazine wasnot disclosed.

Mehvar et al. (Drug Metabolism and Disposition (1987), 15:2, 250-255)describes studies of the pharmacokinetics of tetrabenazine anddihydrotetrabenazine following administration of tetrabenazine to fourpatients affected by tardive dyskinesia. Oral administration oftetrabenazine resulted in low plasma concentrations of tetrabenazine butrelatively high concentrations of dihydrotetrabenazine. However, thestereochemistry of the dihydrotetrabenazine formed in vivo was notreported.

Roberts et al. (Eur. J. Clin. Pharmacol. (1986), 29: 703-708) describesthe pharmacokinetics of tetrabenazine and its hydroxy-metabolite inpatients treated for involuntary movement disorders. Roberts et al.reported that tetrabenazine was extensively metabolised after oraladministration resulting in very low plasma concentrations oftetrabenazine but much higher concentrations of a hydroxymetabolite.Although they did not describe the identity of the hydroxymetabolites,they suggested that the high plasma concentrations of thehydroxymetabolites may be therapeutically important (since themetabolites were known to be pharmacologically active) and that, in viewof the disclosure in Schwartz et al. (idem), the combination of cis andtrans isomers (i.e. alpha and beta isomers) could be moretherapeutically important than the parent drug.

Michael Kilbourn and collaborators at the University of Michigan MedicalSchool have published a number of studies relating to the variousisomers of dihydrotetrabenazines. In Med. Chem. Res. (1994), 5:113-126,Kilbourn et al. describe the use (+/−)-α-[11C]-dihydrotetrabenazine asin vivo imaging agents for VMAT2 binding studies.

In Eur. J. Pharmacol (1995) 278, 249-252, Kilbourn et al. reportedcompetition binding studies using [3H]-tetrabenazine to study the invitro binding affinity of (+)−, (−)−, and (+/−)-α-DHTBZ. The bindingassays gave a Ki value of 0.97 nM for (+)-α-dihydrotetrabenazine and 2.2μM for (−)-α-dihydrotetrabenazine, thereby showing that the (+) alphaisomer has much greater binding affinity for the VMAT2 receptor than the(−) alpha isomer. However, no studies were reported, or conclusionsdrawn, as to the usefulness of either isomer in the treatment ofmovement disorders such as Tourette's syndrome.

In Chirality (1997) 9:59-62, Kilbourn et al. described studies aimed atidentifying the absolute configuration of (+)-α-dihydrotetrabenazinefrom which they concluded that it has the 2R, 3R, 11bR configurationshown above. They also referred to the Schwartz et al. and Mehvar et al.articles discussed above as indicating that the α- andβ-dihydrotetrabenazines are likely to be the pharmacologically activeagents in the human brain but they drew no explicit conclusions as tothe precise stereochemical identities of the active metabolites oftetrabenazine.

In Synapse (2002), 43:188-194, Kilbourn et al. described the use of(+)-α-[11C]-dihydrotetrabenazine as an agent used to measure specific invivo binding of the

VMAT receptor, in “infusion to equilibrium methods”. They found that(−)-α-[11C]-dihydrotetrabenazine produced a uniform brain distribution,consistent with the earlier observations that this enantiomer has a lowVMAT affinity.

Sun et al. (idem) investigated the VMAT2 binding affinities of all eightdihydrotetrabenazine isomers. They found that all of the dextrorotatoryenantiomers exhibited dramatically more potent VMAT2 binding activitythan their corresponding laevorotatory enantiomers with the most active(+)-α-isomer being found to be the most active. However, Sun et al. didnot carry out any investigations into the relative efficacies of theindividual isomers in treating movement disorders such as Tourette'ssyndrome.

WO 2011/153157 (Auspex Pharmaceutical, Inc.) describes deuterated formsof dihydrotetrabenazine. Many deuterated forms of dihydrotetrabenazineare depicted but the application only provides sufficient information toallow a small number of the depicted compounds to be synthesised.Although racemic mixtures of d₆-α-dihydrotetrabenazine andd₆-β-dihydrotetrabenazine as disclosed, these mixtures were not resolvedand the properties of the individual (+) and (−) isomers are notstudied. Similarly, WO 2014/047167 (Auspex Pharmaceutical, Inc.)describes number of deuterated forms of tetrabenazine and itsderivatives. Again, the individual (+) and (−) isomers of deuteratedforms of α- and β-dihydrotetrabenazine were not separated or studied.

WO 2006/053067 (Prestwick) described the use of combinations ofamantadine and tetrabenazine for treating hyperkinetic movementdisorders. Although the document is primarily concerned with usingtetrabenazine, it is envisaged that amantadine can be administered witha “tetrabenazine compound” which may be tetrabenazine ordihydrotetrabenazine.

The Examples section of the patent application only disclosesexperimental protocols of how the combinations of amantadine andtetrabenazine could be administered. Based on the wording of theExamples section, it appears that the combinations had not beenadministered at the time the application was filed and the applicationcontains no results demonstrating the efficacy of combinations ofamantadine and tetrabenazine.

In addition, the Examples section only describes the use oftetrabenazine rather than any dihydrotetrabenazine isomers.

It is evident that, up to the present, it has been unclear as toprecisely which dihydrotetrabenazine isomers are responsible for thetherapeutic properties resulting from the administration oftetrabenazine. It has previously been assumed that(+)-α-dihydrotetrabenazine is the metabolite of tetrabenazine that isprimarily responsible for its therapeutic effects (see WO 2015/171802Neurocrine Biosciences, Inc.), but this has not been demonstratedexperimentally.

As discussed above, the studies carried out by Schwartz et al. (referredto above) demonstrated that both alpha and beta isomers of tetrabenazineare formed as metabolites of tetrabenazine. However, the precisestereochemical configurations of the alpha and beta isomers were notinvestigated.

Studies in human subjects carried out by the present applicants anddescribed in Example 1 below have confirmed the findings of Schwartz etal. that major metabolites of tetrabenazine are indeed alpha and betadihydrotetrabenazines.

However, contrary to what has previously been suggested, the mainmetabolites produced upon administration of tetrabenazine are the(−)-α-dihydrotetrabenazine isomer, which is essentially active as aVMAT2 binding agent, and the (+)-β-dihydrotetrabenazine isomer, which issignificantly less active than the (+)-α-dihydrotetrabenazine isomer.

Thus, in a single dose study involving the administration oftetrabenazine to adult male humans, the C_(max) figures for(+)-β-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine respectivelywere 103 and 72.94 ng/ml whereas the C_(max) figures for(−)β-dihydrotetrabenazine and (+)-α-dihydrotetrabenazine respectivelywere 5.28 and 2.61 ng/ml. The area under the curve (AUC) figures foreach of the (+)-β-dihydrotetrabenazine, (−)-α-dihydrotetrabenazine,(−)-β-dihydrotetrabenazine and (+)-α-dihydrotetrabenazine metabolitesrespectively were 375.78, 305.84, 16.28 and 7.98. A similar distributionof metabolites was found when multiple doses of tetrabenazine wereadministered.

The data suggest that (+)-α-dihydrotetrabenazine is not primarilyresponsible for the therapeutic properties of tetrabenazine. On thecontrary, it appears that (+)-α-dihydrotetrabenazine may be responsiblefor a relatively small contribution to the therapeutic properties oftetrabenazine.

The importance of preparing enantiopure compositions for treatment ofthe human and animal body is known. It is well known that enantiomersmay have different biological properties, for example wherein oneenantiomer is useful for the treatment of a specific disease orcondition and wherein the other enantiomer is toxic or produces unwantedside effects. An example of this is the drug thalidomide, which wasmarketed as a sedative and also prescribed to pregnant women to treatmorning sickness, but it was later found that one enantiomer causedbirth defects in children of the women who had been administeredthalidomide during their pregnancy.

Guidance from the FDA regarding enantiomers states that applications fordrug substances and drug products should include a stereochemicallyspecific identity test and/or a stereochemically selective assay method.

Even in cases where one of the enantiomers is medically useful and theother is inactive and shows no side effects, it may still beadvantageous to remove the inactive enantiomer in order to reduce thesize of the dosage form administered to patients.

SUMMARY OF THE INVENTION

It has now surprisingly been found that combinations of (+)- and(−)-α-dihydrotetrabenazine are more effective in the reduction oflocomotor activity in amphetamine induced rats than(+)-α-dihydrotetrabenazine alone, despite the fact that it has beenpreviously reported that the (−)-α-dihydrotetrabenazine is a poor VMAT2inhibitor.

It has also been shown that both racemic and scalemic (i.e. non-racemic)combinations exhibit enhanced efficacy

Studies confirmed the inactivity of (−)-α-dihydrotetrabenazine intreating movement disorders when administered alone (see Example 2,Study 1). However, it was unexpectedly found that when(−)-α-dihydrotetrabenazine was administered in combination with(+)-α-dihydrotetrabenazine, an improved effect was seen when compared tothe administration of the (+)-isomer alone (see Example 2, Studies 3 and4). It is thought that this improved effect may be due to the binding of(−)-α-dihydrotetrabenazine to proteins other than VMAT2, which may playa role in mediating hyperkinetic movement disorders.

On the basis of the studies carried out to date, it is envisaged thatcombinations of (+)- and (−)-α-dihydrotetrabenazine will be useful inthe prophylaxis or treatment of the disease states and conditions forwhich tetrabenazine is currently used or proposed. Thus, by way ofexample, and without limitation, the dihydrotetrabenazine compounds ofthe invention may be used for the treatment of movement disorders and inparticular hyperkinetic movement disorders such as Huntington's disease,hemiballismus, senile chorea, tic disorders, tardive dyskinesia,dystonia and Tourette's syndrome.

Accordingly, in a first aspect, the invention provides a pharmaceuticalunit dosage form comprising (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine, or pharmaceutically acceptable saltsthereof, and a pharmaceutically acceptable excipient.

In another aspect, the invention provides a combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof, for use in medicine.(+)-α-Dihydrotetrabenazine is believed to have the chemical structure(I) shown below:

(−)-α-Dihydrotetrabenazine is believed to have the chemical structure(II) shown below:

In another aspect, the invention provides a combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof, for use in medicine.

In a further aspect, the invention provides a combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof (pharmaceutical unit dosageform as hereinbefore defined), for use in the treatment of a movementdisorder.

In further embodiments, the invention provides:

-   -   A method of treatment of a movement disorder in a subject in        need thereof (e.g. a mammalian subject such as a human), which        treatment comprises administering to the subject a combination        of (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, or        pharmaceutically acceptable salts thereof.    -   The use of a combination of (+)-α-dihydrotetrabenazine and        (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable salts        thereof, for the manufacture of a medicament for the treatment        of a movement disorder.

The inventors have also found that low doses (i.e. of 20 mg or less perday) of (+)-α-dihydrotetrabenazine may be useful in the treatment ofmovement disorders and it is therefore envisaged that such low doses of(+)-α-dihydrotetrabenazine, in combination with(−)-α-dihydrotetrabenazine, will also be useful in treating movementdisorders.

Accordingly, in another embodiment, the invention provides a combinationof (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof, for use in a method oftreatment of a movement disorder, wherein the method comprisesadministering to a subject (.e.g. a human subject) in need thereof aneffective therapeutic amount of the combination sufficient to provide adosage of from 1 mg to 20 mg of (+)-α-dihydrotetrabenazine per day.

In further aspects, the invention provides:

-   -   A method of treatment of movement disorders, wherein the method        comprises administering to a subject (.e.g. a human subject) in        need thereof an effective therapeutic amount of a combination of        (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, or        pharmaceutically acceptable salts thereof, sufficient to provide        a dosage of from 1 mg to 20 mg of (+)-α-dihydrotetrabenazine per        day.    -   The use of a combination of (+)-α-dihydrotetrabenazine and        (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable salts        thereof, for the manufacture of a medicament for the treatment        of a movement disorder, wherein the method comprises        administering to a subject (.e.g. a human subject) in need        thereof an effective therapeutic amount of the combination        sufficient to provide a dosage of from 1 mg to 20 mg of        (+)-α-dihydrotetrabenazine per day.    -   The use of a (−)-α-dihydrotetrabenazine, or a pharmaceutically        acceptable salt thereof, for the manufacture of a medicament for        administration in combination with (+)-α-dihydrotetrabenazine or        a pharmaceutuically acceptable salt thereof for a method of        treatment of a movement disorder, wherein the method comprises        administering to a subject (.e.g. a human subject) in need        thereof an effective therapeutic amount of the combination        sufficient to provide a dosage of from 1 mg to 20 mg of        (+)-α-dihydrotetrabenazine per day.

In each of the foregoing embodiments (i.e. a combination for use, amethod, or a use) employing a low dose of (+)-α-dihydrotetrabenazine ora pharmaceutically acceptable salt thereof, the daily dose of(+)-α-dihydrotetrabenazine is from 1 mg to 20 mg.

In particular embodiments, there is provided

-   -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 1.5 mg to 20 mg (e.g.        between 1.5 mg and 20 mg) per day.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 2 mg to 20 mg (e.g.        between 2 mg and 20 mg) per day.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 3 mg to 20 mg (e.g.        between 3 mg and 20 mg) per day.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 2 mg to 15 mg (e.g.        between 2 mg and 15 mg) per day.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 3 mg to 15 mg (e.g.        between 3 mg and 15 mg) per day.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of (+)-α-dihydrotetrabenazine from 5 mg to 15 mg (e.g.        between 5 mg and 15 mg) per day.

The administration of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine typically forms part of a chronic treatmentregime. The (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazinemay therefore be administered to a patient for a treatment period of atleast a week, more usually at least two weeks, or at least a month, andtypically longer than a month. Where a patient is shown to respond wellto treatment, the period of treatment can be longer than six months andmay extend over a period of years.

The chronic treatment regime may involve the administration of the(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine every day, orthe treatment regime may include days when no (+)-α-dihydrotetrabenazineor (−)-α-dihydrotetrabenazine is administered.

The dosage administered to the subject may vary during the treatmentperiod. For example, the initial dosage may be increased or decreaseddepending on the subject's response to the treatment. A subject may, forexample, be given an initial low dose to test the subject's tolerancetowards the (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine,and the dosage thereafter increased as necessary up to the maximum dailyintake of 20 mg. Alternatively, an initial daily dosage administered tothe patient may be selected so as to give an estimated desired degree ofVMAT2 blockage, following which a lower maintenance dose may be givenfor the remainder of the treatment period, with the option of increasingthe dosage should the subject's response to the treatment indicate thatan increase is necessary.

It is envisaged that the quantity of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine required to achieve the desired therapeuticeffect will be dependent on the weight of the subject to be treated. Thequantities of (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazineadministered to the subject can be expressed in a number of mg/kg, wherein the kg relates the weight of the subject to be treated. Theappropriate dosage amount can therefore be calculated by multiplying themg/kg amount by the weight of the subject to be treated.

Accordingly, in another aspect, the invention provides a combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine orpharmaceutically acceptable salts thereof, for use in a method for thetreatment of a movement disorder, wherein the treatment comprisesadministering to a subject an amount of the combination of from 0.01mg/kg to 0.3 mg/kg (e.g. between 0.01 mg/kg and 0.3 mg/kg) per dayprovided that the total amount of (+)-α-dihydrotetrabenazineadministered per day is in the range from 1 mg to 20 mg.

In further aspects, the invention provides:

-   -   A method of treatment of a movement disorder in a subject in        need thereof (e.g. a mammalian subject such as a human), which        treatment comprises administering to the subject a combination        of (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, or        pharmaceutically acceptable salts thereof, in an amount from        0.01 mg/kg to 0.3 mg/kg (e.g. between 0.01 mg/kg and 0.3 mg/kg)        per day, provided that the total amount of        (+)-α-dihydrotetrabenazine administered per day is in the range        from 1 mg to 20 mg.    -   The use of a combination of (+)-α-dihydrotetrabenazine and        (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable salts        thereof for the manufacture of a medicament for the treatment of        a movement disorder, which treatment comprises administering to        the subject the combination in an amount from 0.01 mg/kg to 0.3        mg/kg (e.g. between 0.01 mg/kg and 0.3 mg/kg), provided that the        total amount of (+)-α-dihydrotetrabenazine administered per day        is in the range from 1 mg to 20 mg.

In each of the foregoing embodiments (i.e. a combination for use, amethod, or a use) wherein a combination of (+)-α-dihydrotetrabenazineand (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable saltsthereof, is administered in an amount from 0.01 mg/kg to 0.3 mg/kg (e.g.between 0.01 mg/kg and 0.3 mg/kg) per day, the daily dose of(+)-α-dihydrotetrabenazine is from 1 mg to 20 mg.

In particular embodiments, there is provided:

-   -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination of from 0.02 mg/kg to 0.3 mg/kg (e.g.        between 0.02 mg/kg and 0.3 mg/kg) per day, provided that the        total amount of (+)-α-dihydrotetrabenazine administered per day        is in the range from 1 mg to 20 mg.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination of from 0.03 mg/kg to 0.3 mg/kg (e.g.        between 0.03 mg/kg and 0.3 mg/kg) per day, provided that the        total amount of (+)-α-dihydrotetrabenazine administered per day        is in the range from 1 mg to 20 mg.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination from 0.04 mg/kg to 0.3 mg/kg (e.g.        between 0.04 mg/kg and 0.3 mg/kg) per day, provided that the        total amount of (+)-α-dihydrotetrabenazine administered per day        is in the range from 1 mg to 20 mg.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination from 0.05 mg/kg to 0.3 mg/kg (e.g.        between 0.05 mg/kg and 0.3 mg/kg) of (+)-α-dihydrotetrabenazine,        provided that the total amount of (+)-α-dihydrotetrabenazine        administered per day is in the range from 1 mg to 20 mg.

The combinations of the invention (and dosage forms containing thecombinations) are useful in the treatment of movement disorders, and inparticular hyperkinetic movement disorders such as Huntington's disease,hemiballismus, senile chorea, tic disorders, tardive dyskinesia,dystonia and Tourette's syndrome.

More particularly, the combinations of the invention (and dosage formscontaining the combinations) are for use in the treatment of ahyperkinetic movement disorder selected from tic disorders, tardivedyskinesia and Tourette's syndrome.

In one particular embodiment, the combinations of the invention (anddosage forms containing the combinations) are for use in the treatmentof tardive dyskinesia.

In another particular embodiment, the combinations of the invention (anddosage forms containing the combinations) are for use in the treatmentof Tourette's syndrome.

The usefulness of the combinations of the invention in the treatment ofmovement disorders arises in part from the ability of(+)-α-dihydrotetrabenazine to bind to the vesicular monoaminetransporter 2 (VMAT2).

Complete blocking of the VMAT2 proteins is considered undesirable asthis can lead to unwanted side effects, such as Parkinsonism. Thepresent invention provides plasma levels of (+)-α-dihydrotetrabenazineand (−)-α-dihydrotetrabenazine that are sufficient to give effectivetreatment of movement disorders but do not block the VMAT2 proteins toan extent that causes Parkinsonism and similar side effects. The levelsof VMAT2 blocking can be determined by competitive binding studies usingPositron Emission Tomography (PET). By co-administering a radioactiveligand with the compound of interest at various concentrations, theproportion of binding sites occupied can be determined (see for example,Matthews et al., “Positron emission tomography molecular imaging fordrug development”, Br. J. Clin. Pharmacol., 73:2, 175-186).

Accordingly, in a further aspect, the invention provides a combinationof (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof, for use in a method for thetreatment of a movement disorder, wherein the treatment comprisesadministering to a subject an amount of the combination sufficient tocause a level of blocking of from 20% to 90% of VMAT2 proteins in thesubject.

In further aspects, the invention provides:

-   -   A method of treatment of a movement disorder in a subject in        need thereof (e.g. a mammalian subject such as a human), which        treatment comprises administering to the subject a combination        of (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, or        pharmaceutically acceptable salts thereof, sufficient to cause a        level of blocking of from 20% to 90% of the VMAT2 proteins in        the subject.    -   The use of a combination of (+)-α-dihydrotetrabenazine and        (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable salts        thereof, for the manufacture of a medicament for the treatment        of a movement disorder in a subject (e.g. a mammalian subject        such as a human), which treatment comprises administering to the        subject an amount of the combination sufficient to cause a level        of blocking of from 20% to 90% of VMAT2 proteins in the subject.    -   The use of (+)-α-dihydrotetrabenazine, or a pharmaceutically        acceptable salt thereof, for the manufacture of a medicament for        use in combination with (−)-α-dihydrotetrabenazine or a        pharmaceutically acceptable salt thereof for the treatment of a        movement disorder in a subject (e.g. a mammalian subject such as        a human), which treatment comprises administering to the subject        an amount of the combination sufficient to cause a level of        blocking of from 20% to 90% of VMAT2 proteins in the subject.

In further embodiments, there is provided:

-   -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 25% to 85% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 30% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 35% to 75% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 35% to 70% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 40% to 75% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of from 45% to 75% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of from 35% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of from 40% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 45% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 50% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of from 55% to 80% of the VMAT2 proteins in the        subject.    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject an        amount of the combination sufficient to cause a level of        blocking of VMAT2 proteins in the subject of from 30% to 70%        (e.g. between 30% and 70%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a        blocking level of VMAT2 proteins in the subject of from 30% to        65% (e.g. between 30% and 65%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a        blocking level of VMAT2 proteins in the subject of from 30% to        60% (e.g. between 30% and 60%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        blocking of VMAT2 proteins in the subject of from 40% to 80%        (e.g. between 40% and 80%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of VMAT2 proteins in the subject of from 40% to 75%        (e.g. between 40% and 75%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of VMAT2 proteins in the subject of from 40% to 70%        (e.g. between 40% and 70%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        of blocking of VMAT2 proteins in the subject of from 40% to 65%        (e.g. between 40% and 65%).    -   A combination for use, a method or a use as described herein,        wherein the treatment comprises administering to the subject in        need thereof, wherein the method comprising administering to a        subject an amount of the combination sufficient to cause a level        blocking of VMAT2 proteins in the subject of from 40% to 60%        (e.g. between 40% and 60%).

In each of the foregoing aspects and embodiments of the invention, thecombinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine may be racemic.

Alternatively, in each of the foregoing aspects and embodiments of theinvention, the combinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine may be scalemic (i.e. non-racemic).

In each of the combinations of the invention, the uses thereof andpharmaceutical dosage forms containing the combinations, as definedabove, the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine in the combination can be, for example, from0.5:1 to 20:1. In particular embodiments, the ratio of(+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine in thecombination can be a ratio in a range selected from:

(i) 1:1 to 20:1

(ii) 1:1 to 15:1

(iii) 1:1 to 12:1

(iv) 1:1 to 10:1

(v) 1:1 to 5:1

(vi) 1:1 to 4:1

(vii) 1:1 to 3:1

(viii) 1:1 to 2:1

(ix) 1.1:1 to 20:1

(x) 1.1:1 to 15:1

(xi) 1.1:1 to 12:1

(xii) 1.1:1 to 10:1

(xiii) 1.1:1 to 5:1

(xiv) 1.1:1 to 4:1

(xv) 1.1:1 to 3:1

(xvi) 1.1:1 to 2:1

(xvii) 1.2:1 to 20:1

(xviii) 1.2:1 to 15:1

(xix) 1.2:1 to 12:1

(xx) 1.2:1 to 10:1

(xxi) 1.2:1 to 5:1

(xxii) 1.2:1 to 4:1

(xxiii) 1.2:1 to 3:1

(xxiv) 1.2:1 to 2:1

In each of the foregoing aspects and embodiments of the invention, thecombinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine are typically unaccompanied by otherdihydrotetrabenazine isomers.

In some embodiments, minor amounts of other tetrabenazine isomers may bepresent but these generally are present in amounts corresponding to nomore than 20% by weight (i.e. 0.2:1), compared to the total weight ofthe combination. More usually, other dihydrotetrabenazine isomers arepresent in amounts corresponding to no more than 10% or 5%, or 2%, or 1%by weight (i.e. 0.2:1), compared to the total weight of the combination.

In each of the foregoing aspects and embodiments of the inventionrelating to combinations of (+)-α-dihydrotetrabenazine or(−)-α-dihydrotetrabenazine or pharmaceutically acceptable salts thereof,typically, the (+)-α-dihydrotetrabenazine or (−)-α-dihydrotetrabenazineor pharmaceutically acceptable salt thereof, are not administered with atherapeutically effective amount of amantadine. More particularly, the(+)-α-dihydrotetrabenazine or (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salt thereof, are not administered with anyamount of amantadine.

For example, with reference to pharmaceutical unit dosage forms,typically the unit dosage form does not comprise a therapeuticallyeffective amount of amantadine and, more particularly, thepharmaceutical unit dosage form does not comprise any amount ofamantadine.

Furthermore, in each of the foregoing aspects and embodiments of theinvention relating to (+)-α-dihydrotetrabenazine or(−)-α-dihydrotetrabenazine or pharmaceutically acceptable salts thereof,the pharmaceutical unit dosage form may be other than an extendedrelease or delayed release dosage form.

Thus, for example, the (+)-α-dihydrotetrabenazine or(−)-α-dihydrotetrabenazine, or pharmaceutically acceptable salt thereof,may be administered as an immediate release unit dosage form.

In each of the foregoing aspects and embodiments, the(+)-α-dihydrotetrabenazine and/or (−)-α-dihydrotetrabenazine can beadministered as the free base or as a pharmaceutically acceptable salt.In one embodiment, one or both of the (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine are administered as pharmaceuticallyacceptable salts. In another embodiment, both the(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine areadministered as free bases. Unless stated otherwise, or unless thecontext indicates otherwise, the quantities of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine are calculatedas the amounts of the free base, or when the (+)-α-dihydrotetrabenazineor (−)-α-dihydrotetrabenazine is in the form of a pharmaceuticallyacceptable salt, the amount of (+)-α-dihydrotetrabenazine or(−)-α-dihydrotetrabenazine per se present in the pharmaceuticallyacceptable salt.

All references herein to (+)-α-dihydrotetrabenazine include(+)-α-dihydrotetrabenazine both the free base and salts thereof, unlessthe context indicates otherwise. Likewise all references herein to(−)-α-dihydrotetrabenazine include (−)-α-dihydrotetrabenazine both thefree base and salts thereof, unless the context indicates otherwise

The salts are typically acid addition salts.

The salts can be synthesized from the parent compound by conventionalchemical methods such as methods described in Pharmaceutical Salts:Properties, Selection, and Use, P. Heinrich Stahl (Editor), Camille G.Wermuth (Editor), ISBN: 3-90639-026-8, Hardcover, 388 pages, August2002. Generally, such salts can be prepared by reacting the free baseform of the compound with the acid in water or in an organic solvent, orin a mixture of the two; generally, nonaqueous media such as ether,acetone, ethyl acetate, ethanol, isopropanol, or acetonitrile are used.

Acid addition salts may be formed with a wide variety of acids, bothinorganic and organic. Examples of acid addition salts include saltsformed with an acid selected from the group consisting of acetic,2,2-dichloroacetic, adipic, alginic, ascorbic (e.g. L-ascorbic),L-aspartic, benzenesulphonic, benzoic, 4-acetamidobenzoic, butanoic, (+)camphoric, camphor-sulphonic, (+)-(1S)-camphor-10-sulphonic, capric,caproic, caprylic, cinnamic, citric, cyclamic, dodecylsulphuric,ethane-1,2-disulphonic, ethanesulphonic, 2-hydroxyethanesulphonic,formic, fumaric, galactaric, gentisic, glucoheptonic, D-gluconic,glucuronic (e.g. D-glucuronic), glutamic (e.g. L-glutamic),α-oxoglutaric, glycolic, hippuric, hydrobromic, hydrochloric, hydriodic,isethionic, (+)-L-lactic, (±)-DL-lactic, lactobionic, maleic, malic,(−)-L-malic, malonic, (±)-DL-mandelic, methanesulphonic,naphthalene-2-sulphonic, naphthalene-1,5-disulphonic,1-hydroxy-2-naphthoic, nicotinic, nitric, oleic, orotic, oxalic,palmitic, pamoic, phosphoric, propionic, L-pyroglutamic, salicylic,4-amino-salicylic, sebacic, stearic, succinic, sulphuric, tannic,(+)-L-tartaric, thiocyanic, p-toluenesulphonic, undecylenic and valericacids, as well as acylated amino acids and cation exchange resins.

The salt forms of the compounds of the invention are typicallypharmaceutically acceptable salts, and examples of pharmaceuticallyacceptable salts are discussed in Berge et al., 1977, “PharmaceuticallyAcceptable Salts,” J. Pharm. Sci., Vol. 66, pp. 1-19. However, saltsthat are not pharmaceutically acceptable may also be prepared asintermediate forms which may then be converted into pharmaceuticallyacceptable salts. Such non-pharmaceutically acceptable salts forms,which may be useful, for example, in the purification or separation ofthe compounds of the invention, also form part of the invention.

The (+)-α-dihydrotetrabenazine and/or (−)-α-dihydrotetrabenazine maycontain one or more isotopic substitutions, and a reference to aparticular element includes within its scope all isotopes of theelement. For example, a reference to hydrogen includes within its scope¹H, ²H (D), and ³H (T). Similarly, references to carbon and oxygeninclude within their scope respectively 11C, ¹²C, ₁₃C and ¹⁴C and ¹⁶Oand ¹⁸O.

Typically, the (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazineof the invention does not contain isotopes (such as ¹¹C or ³H) inamounts higher than their natural abundance.

In one embodiment, the percentage of the total hydrogen atoms in the(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine that aredeuterium atoms is less than 2%, more typically less than 1%, moreusually less than 0.1%, preferably less than 0.05% and most preferablyno more than 0.02%.

In an analogous manner, a reference to a particular functional groupalso includes within its scope isotopic variations, unless the contextindicates otherwise.

The isotopes may be radioactive or non-radioactive. In one embodiment ofthe invention, the (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine contains no radioactive isotopes. Suchcompounds are preferred for therapeutic use. In another embodiment,however, the (+)-α-dihydrotetrabenazine and/or(−)-α-dihydrotetrabenazine may contain one or more radioisotopes.Compounds containing such radioisotopes may be useful in a diagnosticcontext.

References to (+)-α-dihydrotetrabenazine and and(−)-α-dihydrotetrabenazine include any solvates formed by the compounds.

Examples of solvates are solvates formed by the incorporation into thesolid state structure (e.g. crystal structure) of the compounds of theinvention of molecules of a non-toxic pharmaceutically acceptablesolvent (referred to below as the solvating solvent). Examples of suchsolvents include water, alcohols (such as ethanol, isopropanol andbutanol) and dimethylsulphoxide. Solvates can be prepared byrecrystallising the compounds of the invention with a solvent or mixtureof solvents containing the solvating solvent. Whether or not a solvatehas been formed in any given instance can be determined by subjectingcrystals of the compound to analysis using well known and standardtechniques such as thermogravimetric analysis (TGA), differentialscanning calorimetry (DSC) and X-ray crystallography.

The solvates can be stoichiometric or non-stoichiometric solvates.

Particular examples of solvates are hydrates such as hemihydrates,monohydrates and dihydrates.

For a more detailed discussion of solvates and the methods used to makeand characterise them, see Bryn et al., Solid-State Chemistry of Drugs,Second Edition, published by SSCI, Inc of West Lafayette, Ind., USA,1999, ISBN 0-967-06710-3.

Alternatively, rather than existing as a hydrate, the compound of theinvention may be anhydrous. Therefore, in another embodiment, either orboth of the (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazineare in an anhydrous form.

Methods for the Preparation of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine)

(+)-α-Dihydrotetrabenazine and (−)-α-dihydrotetrabenazine can beprepared from tetrabenazine according to the synthetic route shown inScheme 1.

Racemic tetrabenazine(3-isobutyl-9,10-dimethyoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1,a]isoquinolin-2-one)containing the RR and SS isomers of tetrabenazine is reduced with sodiumborohydride to afford a mixture of four dihydrotetrabenazine isomers ofwhich a racemic mixture of the α-dihydrotetrabenazine (RRR and SSSisomers) constitutes the major product and a racemic mixture of theβ-dihydrotetrabenazines (the SRR and RSS isomers) constitutes a minorproduct. The β-dihydrotetrabenazines can be removed during an initialpurification procedure, for example by chromatography orrecrystallization and then the racemic α-dihydrotetrabenazines resolvedby well known methods such as chiral chromatography or the formation ofdiastereoisomeric salts by reaction with chiral acids followed byseparation by recrystallisation.

For example, by recrystallisation of the racemic mixture withdi-p-toluoyl-L-tartaric acid or (R)-(−)-camphorsulfonic acid or bychiral chromatography, the (+)-α-dihydrotetrabenazine isomer (I) ((2R,3R,11bR)-3-isobutyl-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1,a]isoquinolin-2-ol)can be obtained.

By recrystallisation of the racemic mixture with di-p-toluoyl-R-tartaricacid or (L)-(+)-camphorsulfonic acid or by chiral chromatography, the(−)-α-dihydrotetrabenazine isomer (I) ((2S, 3S,11bS)-3-isobutyl-9,10-dimethoxy-1,3,4,6,7,11b-hexahydro-2H-pyrido[2,1,a]isoquinolin-2-ol)can be obtained.

(+)-α-Dihydrotetrabenazine and (−)-α-dihydrotetrabenazine can also beprepared according to Yao et al., “Preparation and evaluation oftetrabenazine enantiomers and all eight stereoisomers ofdihydrotetrabenazine as VMAT2 inhibitors”, Eur. J. Med. Chem., (2011),46, pp. 1841-1848.

Pharmaceutical Formulations and Methods of Treatment

The pharmaceutical unit dosage forms of the invention can be in any formsuitable for oral, parenteral, topical, intranasal, intrabronchial,ophthalmic, otic, rectal, intra-vaginal, or transdermal administration.Where the compositions are intended for parenteral administration, theycan be formulated for intravenous, intramuscular, intraperitoneal,subcutaneous administration or for direct delivery into a target organor tissue by injection, infusion or other means of delivery.

Pharmaceutical unit dosage forms suitable for oral administrationinclude tablets, capsules, caplets, pills, lozenges, syrups, solutions,sprays, powders, granules, elixirs and suspensions, sublingual tablets,sprays, wafers or patches and buccal patches.

Particular examples of pharmaceutical unit dosage forms containing thecombinations of the invention are capsules and tablets.

Pharmaceutical unit dosage forms containing the combinations of theinvention can be formulated in accordance with known techniques, see forexample, Remington's Pharmaceutical Sciences, Mack Publishing Company,Easton, Pa., USA.

Thus, tablet compositions can contain a unit dosage of the combinationof active compounds together with an inert diluent or carrier such as asugar or sugar alcohol, e.g.; lactose, sucrose, sorbitol or mannitol;and/or a non-sugar derived diluent such as sodium carbonate, calciumphosphate, talc, calcium carbonate, or a cellulose or derivative thereofsuch as methyl cellulose, ethyl cellulose, hydroxypropyl methylcellulose, and starches such as corn starch. Tablets may also containsuch standard ingredients as binding and granulating agents such aspolyvinylpyrrolidone, disintegrants (e.g. swellable crosslinked polymerssuch as crosslinked carboxymethylcellulose), lubricating agents (e.g.stearates), preservatives (e.g. parabens), antioxidants (e.g. BHT),buffering agents (for example phosphate or citrate buffers), andeffervescent agents such as citrate/bicarbonate mixtures. Suchexcipients are well known and do not need to be discussed in detailhere.

Capsule formulations may be of the hard gelatin or soft gelatin varietyand can contain the active component in solid, semi-solid, or liquidform. Gelatin capsules can be formed from animal gelatin or synthetic orplant derived equivalents thereof.

The solid dosage forms (e.g.: tablets, capsules etc.) can be coated orun-coated, but typically have a coating, for example a protective filmcoating (e.g. a wax or varnish) or a release controlling coating. Thecoating (e.g. a Eudragit™ type polymer) can be designed to release theactive component at a desired location within the gastro-intestinaltract. Thus, the coating can be selected so as to degrade under certainpH conditions within the gastrointestinal tract, thereby selectivelyrelease the compound in the stomach or in the ileum or duodenum.

Instead of, or in addition to, a coating, the (+)-α-dihydrotetrabenazineand (−)-α-dihydrotetrabenazine, or pharmaceutically acceptable saltsthereof making up the combinations of the invention can be presented ina solid matrix comprising a release controlling agent, for example arelease delaying agent which may be adapted to selectively release thecompound under conditions of varying acidity or alkalinity in thegastrointestinal tract. Alternatively, the matrix material or releaseretarding coating can take the form of an erodible polymer (e.g. amaleic anhydride polymer) which is substantially continuously eroded asthe dosage form passes through the gastrointestinal tract.

Compositions for topical use include ointments, creams, sprays, patches,gels, liquid drops and inserts (for example intraocular inserts). Suchcompositions can be formulated in accordance with known methods.

Compositions for parenteral administration are typically presented assterile aqueous or oily solutions or fine suspensions, or may beprovided in finely divided sterile powder form for making upextemporaneously with sterile water for injection.

Examples of formulations for rectal or intra-vaginal administrationinclude pessaries and suppositories which may be, for example, formedfrom a shaped mouldable or waxy material containing the active compound.

Compositions for administration by inhalation may take the form ofinhalable powder compositions or liquid or powder sprays, and can beadministrated in standard form using powder inhaler devices or aerosoldispensing devices. Such devices are well known. For administration byinhalation, the powdered formulations typically comprise the combinationof (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, orpharmaceutically acceptable salts thereof together with an inert solidpowdered diluent such as lactose.

The (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine, and theirrespective salts can be formulated separately and used in combination,or they can be formulated together. When formulated together, they canbe provided as a mixture to which one or more pharmaceutical excipientsis (are) added before processing (e.g. compressing to form a tablet orfilling into a capsule) to form a pharmaceutical composition such as aunit dosage form. Alternatively, at least some of the(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine can beformulated separately in different granules, pellets, microbeads ormini-tablets and then brought together and processed to give apharmaceutical composition (e.g. by filling into a capsule orcompressing to form a tablet). As another alternative, the(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine can becontained within different layers in a multi-layered tablet. In anotheralternative, the (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine can each be added separately to an excipientor mixture of excipients and then formulated together.

Particular pharmaceutical compositions of the invention are compositionsselected from:

-   -   Sublingual compositions;    -   Intranasal;    -   Pellets or tablets formulated to provide release kinetics        corresponding to zero order release of the active compound;    -   Pellets or tablets formulated to provide first fast release        followed by constant rate release (zero order) of the active        compound;    -   Pellets or tablets formulated to provide a mixture of first        order and zero order release of the active compound; and    -   Pellets or tablets formulated to provide a combination of zero        order and first order release of the active compound; and        optionally a further order of release of the active compound        selected from second, third and fourth orders of release and        combinations thereof.

Pellets and tablets formulated to provide release kinetics of the typesdefined above can be prepared according to methods well known theskilled person; for example as described in Remington's PharmaceuticalSciences (idem) and “Remington — The Science and Practice of Pharmacy,21st edition, 2006, ISBN 0-7817-4673-6.

The combinations of the invention will generally be presented inpharmaceutical unit dosage form and, as such, will typically containsufficient compound to provide a desired level of biological activity,as described above.

The combinations of the invention will be administered to a subject(patient) in need thereof (for example a human or animal patient) in anamount sufficient to achieve the desired therapeutic effect, asdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the average total distance travelled by rats when treatedwith vehicle (with or without amphetamine induction) and(−)-α-dihydrotetrabenazine at a dose of 2.5 mg/kg and risperidone at adose of 1 mg/kg in amphetamine-induced rats, as described in Example 2,Study 1 below.

FIG. 2 shows the average total stereotypic behaviour by rats whentreated with vehicle (with or without amphetamine induction) and(−)-α-dihydrotetrabenazine at a dose of 2.5 mg/kg and risperidone at adose of 1 mg/kg in amphetamine-induced rats, as described in Example 2,Study 1 below.

FIG. 3 shows the average total distance travelled by rats when treatedwith vehicle (with or without amphetamine induction) and(+)-α-dihydrotetrabenazine at doses of 0.1 mg/kg and 0.25 mg/kg andrisperidone at a dose of 1 mg/kg in amphetamine-induced rats, asdescribed in Example 2, Study 2 below.

FIG. 4 shows the average total stereotypic behaviour by rats whentreated with vehicle (with or without amphetamine induction) and(+)-α-dihydrotetrabenazine at doses of 0.1 mg/kg and 0.25 mg/kg andrisperidone at a dose of 1 mg/kg in amphetamine-induced rats, asdescribed in Example 2, Study 2 below.

FIG. 5 shows the average total distance travelled by rats when treatedwith vehicle (with or without amphetamine induction) and(−)-α-dihydrotetrabenazine at a dose of 2 mg/kg, a combination of(+)-α-dihydrotetrabenazine at a dose of 2 mg/kg and(−)-α-dihydrotetrabenazine at a dose of 2 mg/kg, and risperidone at adose of 1 mg/kg in amphetamine-induced rats, as described in Example 2,Study 3 below.

FIG. 6 shows the average total stereotypic behaviour by rats whentreated with vehicle (with or without amphetamine induction) and(−)-α-dihydrotetrabenazine at a dose of 2 mg/kg, a combination of(+)-α-dihydrotetrabenazine at a dose of 2 mg/kg and(−)-α-dihydrotetrabenazine at a dose of 2 mg/kg, and risperidone at adose of 1 mg/kg in amphetamine-induced rats, as described in Example 2,Study 3 below.

FIG. 7 shows the average total distance travelled by rats when treatedwith vehicle (with or without amphetamine induction) and combinations of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine in varyingratios, and risperidone at a dose of 1 mg/kg in amphetamine-inducedrats, as described in Example 2, Study 4 below.

FIG. 8 shows the average total stereotypic behaviour by rats whentreated with vehicle (with or without amphetamine induction) andcombinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine in varying ratios, and risperidone at a doseof 1 mg/kg in amphetamine-induced rats, as described in Example 2, Study4 below.

EXAMPLES

The following non-limiting examples illustrate the synthesis andproperties of the compositions of the invention.

Example 1

An Investigation into the Nature of the Dihydrotetrabenazine MetabolitesFormed After Administration of Tetrabenazine o Human Subjects

A pharmacokinetic study was carried out in healthy adult male volunteersunder fasting conditions at a dose of single and multiple oraladministration of 25 mg tablets once a day to ascertain the plasmalevels of +/-α and +/−αdihydro-tetrabenazine. The data are summarisedbelow.

Table 1 summarises the pharmacokinetic data obtained followingsingle-dose oral administration of tetrabenazine at a dose level of 25mg (fasting, N=08).

TABLE 1 T_(max) Half-life Mean C_(max) AUC(0-t) AUC(0-inf.) K_(el)(Mean) Extrapolated Analyte (h) (ng/mL) (ng · h/mL) (ng · h/mL) NA (h)AUC (%) Tetrabenazine 0.87 0.58 1.87 2.42 0.19 4.35 27.54 (+) α-DHTBZ1.16 2.61 7.98 10.83 0.17 4.79 32.10 (−) α-DHTBZ 0.938 72.94 305.84351.80 0.10 7.89 10.59 (+) β-DHTBZ 1.125 103.00 375.78 410.46 0.13 5.805.03 (−) β-DHTBZ 1.03 5.28 16.28 18.77 0.45 12.98 17.66

Table 2 summarises the pharmacokinetic data obtained followingmultiple-dose oral administration of tetrabenazine at a dose level of 25mg (fasting, N=07).

TABLE 2 T_(maxss) Mean C_(maxss) C_(minss) AUC(0-t) C_(tss) C_(avg)Analyte (h) (ng/mL) (ng/mL) (ng · h/mL) (ng/mL) (ng · h/mL)Tetrabenazine 96.89 0.73 0.01 2.79 0.10 0.12 (+) α-DHTBZ 97.18 3.31 0.0013.74 0.44 0.57 (−) α-DHTBZ 96.96 98.34 5.61 474.17 6.10 19.76 (+)β-DHTBZ 97.11 144.76 5.45 598.76 5.54 24.95 (−) β-DHTBZ 97.11 7.78 0.1625.17 0.57 1.05

The data presented in Tables 1 and 2 demonstrate that, in humans, themajor metabolites are the (−)-α-dihydrotetrabenazine isomer, which isessentially active as a VMAT2 binding agent, and the(+)-β-dihydrotetrabenazine isomer, which is significantly less activethan the (+)-α-dihydrotetrabenazine isomer. (−)13-Dihydrotetrabenazineand (+)-α-dihydrotetrabenazine were shown to be minor metabolites

The data suggest that (+)-α-dihydrotetrabenazine is not primarilyresponsible for the therapeutic properties of tetrabenazine. On thecontrary, it appears that (+)-α-dihydrotetrabenazine may be responsiblefor a relatively small contribution to the therapeutic properties oftetrabenazine.

Example 2

Investigation of the Effect of Combinations of(+)-α-Dihydrotetrabenazine and (−)-α-Dihydrotetrabenazine on LocomotorActivity and Stereotypies in Rats

The effects of combinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine on locomotor activity and stereotypies inrats were investigated and compared to the effects of the individual(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine isomers.

Materials and Methods

Equipment

Open field arena, Med Associates Inc.

Plastic syringes 1 ml, Terumo. Ref: SS-01T1

Animal feeding needle 15 G, Instech Solomon, Cat: 72-4446

Sartorius Mechatronics Scale A22101, Sartorius Weighting Technology,Germany

Needle 27 G Terumo Myjector, 0,5 ml, Ref: 8300010463

Plastic syringes 3 ml, Soft-Ject, Ref: 8300005761

BD Microtainer K2EDTA tubes Ref: 365975

Matrix 0,75 ml, Alphanum Tubes, Thermo Scientific, Ref: 4274

Microplate Devices, Uniplate 24 wells, 10 ml, Ref: 734-1217

Thermo Electron Corp. Heraeus Fresco 17, refrigerated centrifuge

Test Animals

All animal experiments were carried out according to the NationalInstitute of Health (NIH) guidelines for the care and use of laboratoryanimals, and approved by the National Animal Experiment Board, Finland.Male CD (Charles River Laboratories, Germany) at weight range of 200-250g (165-200 g upon arrival) were used for the experiments. Animals werehoused at a standard temperature (22±1° C.) and in a light-controlledenvironment (lights on from 7 am to 8 pm) with ad libitum access to foodand water.

Methods

Locomotor activity of the rats was tested in open field arena. The openfield test was performed during the rat light cycle and under a normallighting evenly distributed to the test chambers. The paths of the ratswere recorded by activity monitor (Med. Associates Inc.).

Dosing the vehicle, amphetamine, (+)-α-DHTBZ, (−)-α-DHTBZ or risperidonewas done prior to LMA test. The rats were placed in the center of thearena, and the path was recorded for 30 minutes. After 30 minutes oftesting vehicle or amphetamine was dosed and the rat was placed in thecenter of the arena, and the path was recorded for 60 minutes, the totaltesting time being 90 minutes.

Endpoint, Blood Samples and Tissue Processing

Within 10 minutes from the end of the test animals were euthanized by anoverdose of CO₂. The terminal blood sample was collected with cardiacpuncture from all compound treated rats from each group excludingvehicle rats. 0.5 ml of blood was collected with syringe attached to 18G needle and moved into precooled K2-EDTA microtubes. The EDTA microtubewas inverted several times to mix up the EDTA and blood. Tubes were thenimmediately put on wet ice and centrifuged (Heraeus Fresco 17) within10-15 minutes of collecting (9.6×1000 G/10×1000 RPM, +4° C. for 2 min),and 200 μl of plasma was collected in 96-tube plates (MatrixTechnologies ScreenMates 0.75 ml Alphanumeric Round-Bottom Storagetubes, PP) on dry ice according to sample map.

After collection of blood the neck was dislocated at the base of theskull. Brain was collected and weighed. Brain weights were recorded andthe brain was frozen on dry ice on the 24 well plate.

The plasma and brain samples were stored at −80° C. on dry ice untilsent for analysis.

Study 1

Animals were grouped as follows:

-   -   Group 1: 10 rats treated with Vehicle (t=0 min) and Vehicle        (t=30 min)    -   Group 2: 10 rats treated with Vehicle (t=0 min) and Amphetamine        (t=30 min)    -   Group 3: 10 rats treated with (−)-α-DHTBZ 2.5 mg/kg (t=0 min)        and Amphetamine (t=30 min)    -   Group 4: 10 rats treated with risperidone 1 mg/kg (t=0 min) and        Amphetamine (t=30 min)

Results

1. Distance Travelled

Rats dosed with either vehicle, (−)-α-DHTBZ 2.5 mg/kg or risperidone 1mg/kg were subjected to LMA testing first for 30 min and then for 60minutes after vehicle or amphetamine challenge. Resulting locomotoractivity was evaluated in 3 min bins and as a total over the testingperiod. The normalised total distance travelled over the testing time ispresented in FIG. 1 .

When compared to the vehicle-vehicle group the vehicle-amphetamine and(−)-α-DHTBZ 2.5 mg/kg were significantly different. When compared tovehicle-amphetamine group the vehicle-vehicle and risperidone 1 mg/kgwere significantly different.

2. Stereotypic Behaviour

Rats dosed with either vehicle, (−)-α-DHTBZ 2.5 mg/kg or risperidone 1mg/kg were subjected to LMA testing first for 30 min and then for 60minutes after vehicle or amphetamine challenge. Resulting stereotypicactivity was evaluated in 3 min bins and as a total over the testingperiod. The normalised total stereotypic behaviour over the testing timeis presented in FIG. 2 .

When compared to the vehicle-vehicle group the vehicle-amphetamine and(−)-α-DHTBZ 2.5 mg/kg were significantly different. When compared tovehicle-amphetamine group the vehicle-vehicle and risperidone 1 mg/kgwere significantly different.

Conclusions

This study evaluated the effect of (−)-α-DHTBZ at dose 2.5 mg/kg andrisperidone at dose 1 mg/kg on amphetamine induced locomotor activity inmale CD rats.

(−)-α-DHTBZ at dose 2.5 mg/kg did not lead to lower locomotor activityor reduced stereotypic behaviour when compared to thevehicle-amphetamine group. The rats dosed with (−)-α-DHTBZ at dose 2.5mg/kg were less focused on what was going on around. The rats dosed with(−)-α-DHTBZ were equally active when compared to the vehicle-amphetaminedosed animals suggesting that (−)-α-DHTBZ does not have a sedativeeffect similar to risperidone.

STUDY 2

The effects on stereotypic behaviour and the distance travelled in ratsfollowing administration of (+)-α-dihydrotetrabenazine dosed at 0.1mg/kg to 0.25 mg/kg, as well as risperidone at 1 mg/kg, were studied.

Animals were grouped as follows:

-   -   Group 1: 10 rats treated with Vehicle (t=0 min) and Vehicle        (t=30 min)    -   Group 2: 10 rats treated with Vehicle (t=0 min) and Amphetamine        (t=30 min)    -   Group 3: 10 rats treated with (+)-α-DHTBZ 0.1 mg/kg (t=0 min)        and Amphetamine (t=30 min)    -   Group 4: 10 rats treated with (+)-α-DHTBZ 0.25 mg/kg (t=0 min)        and Amphetamine (t=30 min)    -   Group 5: 10 rats treated with risperidone 1 mg/kg (t=0 min) and        Amphetamine (t=30 min)

Results

1 Distance Travelled

Rats dosed with either vehicle, (+)-α-DHTBZ 0.1 mg/kg, (+)-α-DHTBZ 0.25mg/kg, or Risperidone 1 mg/kg were subjected to LMA testing first for 30min and then for 60 minutes after vehicle or amphetamine challenge.Resulting locomotor activity was evaluated in 3 min bins and as a totalover the testing period. The normalised total distance travelled overthe testing time is presented in FIG. 3 .

When compared to vehicle-amphetamine group the vehicle-vehicle,(+)-α-DHTBZ 0.25 mg/kg and risperidone 1 mg/kg were significantlydifferent.

Stereotypic Behaviour

Rats dosed with either vehicle, (+)-α-DHTBZ 0.1 mg/kg, (+)-α-DHTBZ 0.25mg/kg, or Risperidone 1 mg/kg were subjected to LMA testing first for 30min and then for 60 minutes after vehicle or amphetamine challenge.Resulting stereotypic activity was evaluated in 3 min bins and as atotal over the testing period. The normalised total stereotypicbehaviour over the testing time is presented in FIG. 4 .

When compared to vehicle-amphetamine group the vehicle-vehicle,(+)-α-DHTBZ 0.1 mg/kg, (+)-α-DHTBZ 0.25 mg/kg and risperidone 1 mg/kgwere significantly different.

Conclusions

This study evaluated the effect of (+)-α-DHTBZ at doses 0.1 mg/kg and0.25 mg/kg and risperidone at dose 1 mg/kg on amphetamine inducedlocomotor activity in male CD rats.

(+)-α-DHTBZ at 0.25 mg/kg and risperidone 1 mg/kg led to lower locomotoractivity when compared to the vehicle-amphetamine group. (+)-α-DHTBZ atboth the tested doses and risperidone 1 mg/kg led to reduced stereotypicbehaviour when compared to the vehicle-amphetamine group.

STUDY 3

Animals were grouped as follows:

Group 1: 10 rats treated with Vehicle (t=0 min) and Vehicle (t=30 min)

Group 2: 10 rats treated with Vehicle (t=0 min) and Amphetamine (t=30min)

Group 3: 10 rats treated with (+)-α-DHTBZ 2 mg/kg (t=0 min) andAmphetamine (t=30 min)

Group 4: 10 rats treated with (+)-α-DHTBZ 2 mg/kg with (−)-α-DHTBZ 2mg/kg (t=0 min) and Amphetamine (t=30 min)

Group 5: 10 rats treated with risperidone 1 mg/kg (t=0 min) andAmphetamine (t=30 min)

Results

1 Distance Travelled

Rats dosed with either vehicle, (+)-α-DHTBZ 2 mg/kg, the combination of(−)-α-DHTBZ 2 mg/kg and (+)-α-DHTBZ 2 mg/kg or Risperidone 1 mg/kg weresubjected to LMA testing first for 30 min and then for 60 minutes aftervehicle or amphetamine challenge. Resulting locomotor activity wasevaluated in 3 min bins and as a total over the testing period. Thenormalised total distance travelled over the testing time is presentedin FIG. 5 .

When compared to the vehicle-vehicle group the vehicle-amphetamine wassignificantly different. When compared to vehicle-amphetamine group thevehicle-vehicle, (+)-α-DHTBZ 2 mg/kg, the combination of (−)-α-DHTBZ 2mg/kg and (+)-α-DHTBZ 2 mg/kg and risperidone 1 mg/kg were significantlydifferent.

2 Stereotypic Behaviour

Rats dosed with either vehicle, (+)-α-DHTBZ 2 mg/kg, the combination of(−)-α-DHTBZ 2 mg/kg and (+)-α-DHTBZ 2 mg/kg or Risperidone 1 mg/kg weresubjected to LMA testing first for 30 min and then for 60 minutes aftervehicle or amphetamine challenge. Resulting stereotypic activity wasevaluated in 3 min bins and as a total over the testing period. Thenormalised total stereotypic behaviour over the testing time ispresented in FIG. 6 .

When compared to vehicle-amphetamine group the vehicle-vehicle,(+)-α-DHTBZ 2 mg/kg, the combination of (−)-α-DHTBZ 2 mg/kg and(+)-α-DHTBZ 2 mg/kg and risperidone 1 mg/kg were significantlydifferent.

Conclusions

This study evaluated the effect of compounds (+)-α-DHTBZ at a dose of 2mg/kg, the combination of (+)-α-DHTBZ and (−)-α-DHTBZ at dose 2 mg/kgand risperidone at dose 1 mg/kg on amphetamine induced locomotoractivity in male CD rats.

(+)-α-DHTBZ at the tested dose, the combination of (+)-α-DHTBZ and(−)-α-DHTBZ at doses 2 mg/kg and risperidone 1 mg/kg led to lowerlocomotor activity when compared to the vehicle-amphetamine group.(+)-α-DHTBZ at the tested dose, the combination of (+)-α-DHTBZ and(−)-α-DHTBZ at doses 2 mg/kg and risperidone 1 mg/kg led to reducedstereotypic behaviour when compared to the vehicle-amphetamine group.

Amphetamine induced locomotor activity was lesser in rats treated withthe combination of (+)-α-DHTBZ and (−)-α-DHTBZ than in rats treated with(+)-α-DHTBZ only, despite it being shown that the (−)-α-isomer providesvery little, if any, reduction induced locomotor activity.

STUDY 4

Animals were grouped as follows:

-   -   Group 1: 10 rats treated with Vehicle (t=0 min) and Vehicle        (t=30 min)    -   Group 2: 10 rats treated with Vehicle (t=0 min) and Amphetamine        (t=30 min)    -   Group 3: 10 rats treated with (+)-α-DHTBZ 0.5 mg/kg (t=0 min)        and (−)-α-DHTBZ 0.5 mg/kg and Amphetamine (t=30 min)    -   Group 4: 10 rats treated with (+)-α-DHTBZ 1.0 mg/kg (t=0 min)        and (−)-α-DHTBZ 0.5 mg/kg and Amphetamine (t=30 min)    -   Group 5: 10 rats treated with (+)-α-DHTBZ 1.0 mg/kg (t=0 min)        and (−)-α-DHTBZ 1.0 mg/kg and Amphetamine (t=30 min)    -   Group 6: 10 rats treated with (+)-α-DHTBZ 1.5 mg/kg (t=0 min)        and (−)-α-DHTBZ 1.0 mg/kg and Amphetamine (t=30 min)

Results

1 Distance Travelled

Rats dosed with either vehicle, the combination of (+)-α-DHTBZ 0.5 mg/kgand (−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 1 mg/kg or the combination of (+)-α-DHTBZ 1.5 mg/kg and(−)-α-DHTBZ 1 mg/kg were subjected to LMA testing first for 30 min andthen for 60 minutes after vehicle or amphetamine challenge. Resultinglocomotor activity was evaluated in 3 min bins and as a total over thetesting period. The normalised total distance travelled over the testingtime is presented in FIG. 7 .

When compared to vehicle-amphetamine group the vehicle-vehicle,(+)-α-DHTBZ, the combination of (+)-α-DHTBZ 0.5 mg/kg and (−)-α-DHTBZ0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and (−)-α-DHTBZ 0.5mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and (−)-α-DHTBZ 1 mg/kgand the combination of (+)-α-DHTBZ 1.5 mg/kg and (−)-α-DHTBZ 1 mg/kgwere significantly different.

Stereotypic Behaviour

Rats dosed with either vehicle, the combination of (+)-α-DHTBZ 0.5 mg/kgand (−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 1 mg/kg or the combination of (+)-α-DHTBZ 1.5 mg/kg and(−)-α-DHTBZ 1 mg/kg were subjected to LMA testing first for 30 min andthen for 60 minutes after vehicle or amphetamine challenge. Resultingstereotypic activity was evaluated in 3 min bins and as a total over thetesting period. The normalised total stereotypic behaviour over thetesting time is presented in FIG. 8 .

When compared to the vehicle-vehicle group the combination of(+)-α-DHTBZ 1 mg/kg and (−)-α-DHTBZ 0.5 mg/kg was significantlydifferent. When compared to vehicle-amphetamine group thevehicle-vehicle, the combination of (+)-α-DHTBZ 0.5 mg/kg and(−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 0.5 mg/kg, the combination of (+)-α-DHTBZ 1 mg/kg and(−)-α-DHTBZ 1 mg/kg and the combination of (+)-α-DHTBZ 1.5 mg/kg and(−)-α-DHTBZ 1 mg/kg were significantly different.

Conclusions

This study evaluated the effect of the combination of (+)-α-DHTBZ and(−)-α-DHTBZ at doses 0.5 mg/kg+0.5 mg/kg, 1 mg/kg+0.5 mg/kg, 1 mg/kg+1mg/kg and 1.5 mg/kg+1 mg/kg on amphetamine induced locomotor activity inmale CD rats.

The combination of (+)-α-DHTBZ and (−)-α-DHTBZ at all the testedcombinations and risperidone 1 mg/kg led to lower locomotor activitywhen compared to the vehicle-amphetamine group. The combination of(+)-α-DHTBZ and (−)-α-DHTBZ at all the tested doses and risperidone 1mg/kg led to reduced stereotypic behaviour when compared to thevehicle-amphetamine group.

It would appear that there are interactions between the (+)-α-DHTBZ and(−)-α-DHTBZ affecting the ability of (+)-α-DHTBZ to block theamphetamine induced hyperactivity.

Comparing the data for rats dosed with a combination of (+)-α-DHTBZ at adose of 1 mg/kg and (−)-α-DHTBZ at a dose of 0.5 mg/kg and rats dosedwith a combination of (+)-α-DHTBZ at a dose of 1 mg/kg and (−)-α-DHTBZat a dose of 1 mg/kg, given the demonstrated lack of efficiency of the(−)-α-isomer in isolation, it would not be expected that increases inthe amount of (−)-α-isomer in the combination treatment would lead to areduction in the locomotor activity in the tested rats.

Comments

Study 1 in Example 2 is consistent with the reported low activity of the(−)-α-isomer of tetrabenazine. Study 2 in Example 2 shows the efficacyof the (+)-α-isomer alone.

Study 3 in Example 2 demonstrates an unexpected improvement in thereduction of movement when a combination of (+)-α-dihydrotetrabenazineand (−)-α-dihydrotetrabenazine is administered compared with the resultsexpected based on the administration of each isomer separately.

Study 4 in Example 2 demonstrates the reduction in movement followingadministration of combinations of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine over a range of doses where both equal andnon-equal amounts of both isomers are administered together.

Equivalents

It will readily be apparent that numerous modifications and alterationsmay be made to the specific embodiments of the invention described abovewithout departing from the principles underlying the invention. All suchmodifications and alterations are intended to be embraced by thisapplication.

The invention claimed is:
 1. A pharmaceutical unit dosage formcomprising a combination of (+)-α-dihydrotetrabenazine and(−)-α-dihydrotetrabenazine, or pharmaceutically acceptable saltsthereof, and a pharmaceutically acceptable excipient, wherein thecombination of (+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazineis a scalemic mixture, wherein the ratio of (+)-α-dihydrotetrabenazineto (−)-α-dihydrotetrabenazine is from 1.1:1 to 20:1.
 2. A pharmaceuticalunit dosage form according to claim 1, wherein the combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine isunaccompanied by any other isomers of dihydrotetrabenazine.
 3. Apharmaceutical unit dosage form according to claim 1 wherein the ratioof (+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine is from1.2:1 to 20:1.
 4. A pharmaceutical unit dosage form according to claim1, wherein the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine is from 1.1:1 to 15:1.
 5. A pharmaceuticalunit dosage form according to claim 1, wherein the ratio of(+)-α-dihydrotetrabenazine to (−)-a-dihydrotetrabenazine is from 1.1:1to 10:1.
 6. A pharmaceutical unit dosage form according to claim 1,wherein the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine is from 1.1:1 to 5:1.
 7. A pharmaceuticalunit dosage form according to claim 1, wherein the ratio of(+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine is from 1.1:1to 4:1.
 8. A pharmaceutical unit dosage form according to claim 1,wherein the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine is from 1.1:1 to 3:1.
 9. A pharmaceuticalunit dosage form according to claim 1, wherein the ratio of(+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine is from 1.2:1to 15:1.
 10. A pharmaceutical unit dosage form according to claim 1,wherein the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine is from 1.2:1 to 10:1.
 11. A pharmaceuticalunit dosage form according to claim 1, wherein the ratio of(+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine is from 1.2:1to 5:1.
 12. A pharmaceutical unit dosage form according to claim 1,wherein the ratio of (+)-α-dihydrotetrabenazine to(−)-α-dihydrotetrabenazine is from 1.2:1 to 4:1.
 13. A pharmaceuticalunit dosage form according to claim 1, wherein the ratio of(+)-α-dihydrotetrabenazine to (−)-α-dihydrotetrabenazine is from 1.2:1to 3:1.
 14. A method of treating a movement disorder in a subject inneed thereof, the method comprising administering to the subject thepharmaceutical unit dosage form according to claim
 1. 15. A methodaccording to claim 14, wherein the method comprises administering to asubject in need thereof an effective therapeutic amount of thepharmaceutical unit dosage form sufficient to provide a dosage of from 1mg to 20 mg of (+)-α-dihydrotetrabenazine per day.
 16. A methodaccording to claim 14, wherein the method comprises administering to asubject an amount of the pharmaceutical unit dosage form of from 0.01mg/kg to 0.3 mg/kg per day provided that the total amount of(+)-α-dihydrotetrabenazine administered per day is in the range from 1mg to 20 mg.
 17. A method according to claim 14, wherein the movementdisorder is a hyperkinetic movement disorder selected from Huntington'sdisease, hemiballismus, senile chorea, tic disorders, tardivedyskinesia, dystonia and Tourette's syndrome.
 18. A method according toclaim 14, wherein the movement disorder is Tourette's syndrome.
 19. Amethod according to claim 14, wherein the method comprises administeringto a subject an amount of the pharmaceutical unit dosage form sufficientto cause a level of blocking of from 20% to 90% of VMAT2 proteins in thesubject.
 20. A method according to claim 14, wherein the combination of(+)-α-dihydrotetrabenazine and (−)-α-dihydrotetrabenazine isunaccompanied by any other isomers of dihydrotetrabenazine.
 21. A methodaccording to claim 14, wherein the subject is a human subject.